When using dried porcini, soak them in hot water for about 15 minutes until softened, then drain well before cooking. You’ll need roughly 13 to 15 grams of dried porcini, or about 130 grams of fresh, to make one full cup of pâté.
If you're making this with fresh porcini, clean the mushriooms by brushing off any dirt, leaves, or pine needles. Avoid washing them, as they absorb water easily. After that slice them, chop the onion, crush the garlic, and roughly chop the parsley.
Warm the olive oil and butter in a large skillet. Add the onion and garlic and stir-fry gently until they become soft and golden.
Add the mushrooms to the pan and season with salt, pepper, marjoram, and a few small rosemary sprigs. Cook over low heat, stirring now and then, until the mushrooms start to release their aroma. Pour in the white wine and let it simmer for a few minutes.
When the mushrooms have cooked down and most of the liquid has evaporated, pour in the cream. Stir until everything is well coated and creamy.
Let the mixture cook for two more minutes, then add the chopped parsley. Take the pan off the heat and allow it to cool slightly.
Move the mixture to a blender, add the walnuts, and blend at medium speed until smooth. You can leave a bit of texture if you like it more rustic and crunchy.
Leave the pâté to rest for a few minutes, then transfer it into a bowl or jar. Chill in the fridge for about an hour until the butter sets and the texture firms up.
If you’re making it ahead, pour a thin layer of melted butter on top to keep the aroma fresh and lock out air. Store in the fridge overnight, it always tastes even better the next day.